1. Field of the Invention
This invention relates to an inking device for supplying ink to a numbering device or a relief imprinting cylinder attached, for example, to a sheet-feed offset printing apparatus.
2. Description of the Prior Art
FIG. 11 is a schematic view showing the entire structure of a prior art sheet-feed offset printing apparatus. Referring to FIG. 11, numeral 1 indicates a plate cylinder, numberal 3 indicates a blanket cylinder, number 5 indicates an impression cylinder, numeral 7 indicates an inker for plate cylinder, number 9 indicates a sheet feeder, and numeral 11 indicates a delivery station. A line pattern transferred from the plate cylinder 1 to the blanket cylinder is imprinted on a sheet of paper supplied from the sheet feeder 9 into and between the blanket cylinder 3 and the impression cylinder 5, and the printed sheet is discharged by the delivery station 11. Further, a number printing unit 17 comprising a numbering device 13 and its ink unit 15 is disposed between the impression cylinder 5 and the delivery station 11, and the sheet discharged from between the blanket cylinder 3 and the impression cylinder 5 is number printed.
Heretofore, in most small-size printing apparatus, the number printing unit 17 is detachably mounted on a printing apparatus main unit 19, and the detaching configuration includes the following two types. In a first type, referring to FIG. 12, the ink unit is configured as a unit so that a numbering shaft 23 and ink unit 15 can be independently attached and detached. In a second type, referring to FIG. 13, the numbering shaft 23 and ink unit 15 are integrally configured into a unit so that the numbering shaft 23 and the ink unit 14 can be attached and detached all at once.
However, the above-described prior art apparatus has had the following problems. First, when adjusting the nip pressure (contact pressure) of a form roller 18, which applies ink to the numbering device 13, there is only a small working space since a distributor roller 21 is disposed closely, which considerably deteriorates the workability of adjustment. In particular, in the first type which has the numbering shaft 23 and the ink unit 15 separately disposed, the nip pressure adjustment must be performed at every mounting of the ink unit 15 on the main unit 19, which leads to an increased preparation time for printing.
Moreover, when the thickness of a sheet to be printed varies, the distance between the centers of the impression cylinder 5 and the numbering shaft (printing shaft) 23 supporting the numbering device 13 must be varied according to the thickness. In such a case, when the center of the numbering shaft 23 is moved, the nip pressure of the form roller 18 to the numbering device 13 is varied, and therefore the nip pressure must be readjusted.
Further, if, as a result of test printing, the mounting position of the numbering device 13 relative to the numbering shaft 23 is to be varied, the ink unit must be removed in the prior art device of FIG. 12. In the prior art device of FIG. 13 in which the numbering shaft 23 and the ink unit 15 are integrally disposed, the entire unit must be removed. Therefore, various adjustments must be made again after the removed components are replaced.
On the other hand, when final printing is completed or when printing operation must be interrupted during final printing, for example, due to a problem in the paper feed, and the rollers must be idled, the distance between the centers of the impression cylinder 5 and the numbering shaft 23 must be expanded in order to prevent adherence of ink onto the impression cylinder 5. However, if the numbering shaft 23 is moved in the direction away from the impression cylinder 5, the numbering shaft 23 is consequently brought closer to the form roller 18, which increases the nip pressure of the form roller 18 to the numbering device 13. This can result in a change in the concentration of the ink or, in an extreme case, the rubber-made form roller 18 may be damaged.
Although the above description is for the case of number printing, the conditions are the same in the case of an imprinting. When a relief printing cylinder is used in place of the numbering device 13 and is attached to a printing shaft which corresponds to the numbering shaft 23, the imprinting operation can be performed.